To be fair, with TF2 there was a period of several months where you would constantly get items while playing, so many people (including myself) had it running 24/7. There were special maps for idle players and everything.

It could just be my phone's steamapp getting it wrong (I'm at work so I can't log into steam right now) but it seems my counters got reset when I lost my old PC - I'm showing zero times for a number of my games that I've reinstalled but haven't played yet.